AbstractVariations in oyster mutagenicity were monitored in a series ofin siturelocation experiments and compared with tissue concentrations of polycyclic aromatic hydrocarbons (PAHs). Oysters (Crassostrea virginica) were relocated among three rivers in the southern Chesapeake Bay and sampled over a 2‐week exposure period. Extracts of oyster tissues were assayed for mutagenic activity by theSalmonella typhimuriummicrosomal test and analyzed for selected PAHs by gas chromatography. Oysters relocated to the polluted Elizabeth River (Norfolk, VA) from a pristine site (Ware River, VA) accumulated mutagenic activity and PAHs within 3 d following relocation. Mutagenicity increased over a 14‐d period while tissue levels of most PAHs stabilized or declined after 3 d. Extracts of native oysters from the Elizabeth River exhibited comparable levels of mutagenic activity as 14‐d relocated oysters. In elimination experiments, PAH levels and mutagenic activity of Elizabeth River oysters decreased following relocation to the Ware River and were not detected after 14 d. Regression analyses did not detect a significant association between slopes of mutagenicity dose‐responses and tissue levels of PAHs. Marginal associations with numbers ofSalmonellarevertants per plate were detected in comparisons with sums of PAH tissue levels, and with tissue levels of benzofluor